1. Field of the Invention
This invention relates to RF MEMS (MicroElectroMechanical Systems) technology and more particularly to MEMS with wafer level interconnection to electronics on low-resistivity substrate material.
2. Background of Invention
RF MEMS technology has been targeted for insertion in a wide range of military applications from multi-band multi-mode communication systems to inertial navigation systems to sensors. In fact, RF MEMS technology insertion plays a major role in numerous current DARPA funded programs such as Ultra Comm and the Airborne Communications Node (ACN).
This technology could be applied to these programs plus new military insertion opportunities such as targeting systems, satellite communications, high speed tactical data link systems, electronic warfare and countermeasure systems, signal intelligence systems, and antenna systems.
This technology could also be applied to consumer electronics applications such as telecommunications (cellular telephone, back-haul, etc.) commercial aircraft, commercial radar, etc. where the distinct performance advantages and small form factor provided by the combination of RF MEMS and silicon germanium (SiGe) or other electronic circuits are desired.
This technology could also be applied to consumer electronics applications such as telecommunications (cellular telephone, back-haul, etc.) commercial aircraft, commercial radar, etc. where the distinct performance advantages and small form factor provided by the combination of RF MEMS and silicon germanium (SiGe) or other electronic circuits are desired.
Many hetero-junction technologies, epitaxial methods, and substrate materials have been considered incompatible. Specifically, RF MEMS fabrication technology has been considered incompatible with silicon germanium (SiGe) fabrication technology. RF MEMS technology requires a high resistivity substrate material to maximize the circuit RF performance. Typically SiGe circuits are processed on low resistivity material.
Raytheon has investigated the integration of RF MEMS circuitry on a low resistivity SiGe substrate using a xe2x80x9cdirect integrationxe2x80x9d (DI) approach. The primary technical challenge associated with direct integration RF MEMS circuitry with sophisticated electronics is overcoming the influence of the low-resistivity substrate material, typically used by SiGe manufacturers, on the insertion loss of the RF MEMS circuit.
Direct integration (DI) was investigated by Raytheon for overcoming the detrimental affects of the low-resistivity substrate on microwave circuitry. DI involves building a second dielectric layer on top of the substrate to serve exclusively as the microwave substrate. DI, however, has a number of technical challenges.
RF MEMS circuits produced by Raytheon require a smooth substrate. This is necessary due to the geometry of the structures being produced. The flatness of the dielectric material for the DI approach is currently unknown. Secondly, the RF performance of the circuit can be limited by the thin microwave dielectric layer.
In accordance with one embodiment of the present invention wafer level interconnect removes the requirements for substrate material as an issue. Each technology processes their circuitry on the required base material and minimizes the need for additional process development. Following initial processing, the two wafers are electrically interconnected with vertical electrical interconnections.
The wafer level interconnect invention will enable the integration of these two (and other) technologies where previously integration through wafer fabrication has been limited by a requirement for differing base substrate materials. This invention may also provide benefits for wafer level packaging of integrated circuits on silicon substrates where the electrical signal must be isolated from the substrate.